Fuel injector with main shot and variable anchor delay

Details Fuel injector with main shot and variable anchor delay Fuel injector with main shot and variable anchor delay

2001-06-26

2004-03-16

Kwon, John (Department: 3747)

Internal-combustion engines

Combustion chamber means having fuel injection only

Using multiple injectors or injections

C123S300000

Reexamination Certificate

active

06705278

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to electronically controlled fuel injection systems and, more particularly, to a method and apparatus for accurately delivering multiple separate fuel injections to the cylinders of an internal combustion engine during a fuel injection event based upon engine operating conditions when the engine experiences an acceleration or when two fuel injection events are separated by a short period of time.
BACKGROUND
Electronically controlled direct fuel injection devices such as electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder in response to an electronic fuel injection signal received from an electronic fuel injection control device (controller) or system. These signals define waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are becoming more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulates, and the release of nitrogen oxides (NOx). Tailoring the electronic fuel injection current signal waveform and the resulting number of injections and the injection rate of fuel to a combustion chamber during a combustion cycle of the cylinder, as well as the quantity and timing of such fuel injections, is one way to improve emissions and meet higher emissions standards. As a result, many different multiple fuel injection techniques, wherein the electronic fuel injection signal waveform comprises a plurality of distinct fuel injection signals, have been utilized to modify the bum characteristics of the combustion process in an attempt to reduce emission and noise levels. Some techniques involve the use of multiple fuel injections into a single cylinder during a single engine operating cycle, and typically involve splitting the total fuel delivery to the cylinder during a particular engine operating cycle into separate fuel injections. Such injections may include a pilot injection, a main injection, and an anchor injection, where three injections of fuel (a three shot injection) are desired to achieve a desired performance. Each of these fuel injections may also be referred to generally as a “shot”. The “control current signal” (electronic fuel injection current signal), also may be referred to simply as a “fuel injection signal” to a fuel injector indicative of an injection or delivery of fuel to the engine.
At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine performance and emissions control. For example, any of a variety of multiple fuel injection techniques may be utilized at certain steady-state engine operating conditions, including low engine speed and low engine load, while other techniques may be utilized at different engine operating conditions requiring high speed or torque. In the past, the controllability of a multiple fuel injection or split injection event has been somewhat restricted by mechanical and other limitations associated with the particular types of injectors utilized. Even with more advanced electronically controlled injectors, during certain engine operating conditions, it is sometimes difficult to accurately control fuel delivery.
As used throughout this disclosure, an “injection event” is defined as the activity, including the injection of one or more shots, that occur in a particular cylinder or combustion chamber during one operating or combustion cycle of the engine (a “cylinder cycle”). For example, one cycle of a four stroke engine for a particular cylinder includes an intake stroke, compression stroke, expansion stroke, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. As used in the art, and throughout this disclosure, an “engine operating cycle” includes the individual cylinder cycles for the cylinders included therein. For example, an engine operating cycle for a six cylinder engine will include six individual cylinder cycles, one for each of the cylinders of the engine (with each cylinder cycle having four strokes, for a total of 24 strokes). Generally, the cylinder cycles overlap, so that the beginning of the next successive cylinder cycle of a particular cylinder might begin prior to the completion of the beginning of the next engine operating cycle.
U.S. Pat. No. 5,901,682 to McGee et al., which is commonly assigned to the Assignee hereof, describes a direct fuel injection compression ignition engine and a process for transitioning between different engine operating modes. The '682 patent describes calculating a weighted average transition fuel rate for smoothly transitioning between operating modes. The '682 patent does not, however, describe transitioning between a mode having a first characteristic injection shape, especially a split injection configuration or mode, and a mode having a second characteristic injection shape, especially a boot injection configuration or mode.
Desired engine performance is not always achieved at all engine speeds and engine load conditions using previously known fuel injection strategies where, based upon engine operating conditions, the injection timing, number and duration of shots, fuel flow rate and the injected fuel volume are determined in order to reduce emissions and improve fuel consumption. As a result, problems such as injecting fuel too rapidly within a given injection event and/or allowing fuel to be injected beyond a desired stopping point can adversely affect system stability, emission outputs and fuel economy.
In a fuel control system for an internal combustion engine in which one or multiple shots may be used in a given injection event and different injection signal waveforms are achievable, it is desirable to control and deliver any number of separate fuel injection shots to a particular cylinder so as to minimize emissions and fuel consumption based upon the operating conditions of the engine at that particular point in time, e.g. changes in speed, load, or ambient conditions. Such strategies may include splitting the fuel injection into two or more separate fuel shots during a particular injection event, advancing the pilot shot during the injection event, and adjusting the timing between the various multiple fuel injection shots in order to achieve desired emissions and desired fuel consumption. In some situations, it is also desirable to rate shape the front end of the fuel delivery to the cylinder to control the burn characteristics of the particular fuel being utilized. However, in some situations the particular shot duration or the fuel quantity for a given shot may be so small that it is not practical to inject the particular shot.
By way of example, during certain acceleration events, not all of the fuel delivered to the engine in the distinct fuel shots of a multi-shot fuel injection event is combusted for a variety of reasons. In one such event where a turbo charger is used, during an acceleration event the air mass delivered to the engine is lower because the turbo charger device associated with the engine has to spin up to deliver a greater quantity of air corresponding to the increase in the fuel. When a rich fuel mixture is introduced into the cylinder, more fuel is likely to contact the cylinder walls than with a comparatively leaner fuel mixture. Because a cylinder's walls are typically cooler in comparison to the interior of the cylinder, the fuel does not combust but instead mixes with the cylinder wall lubricating oil. This fuel deteriorates the lubricating quality of the engine oil and adversely

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